As pressurized materials to be filled into a pressure vessel, various compressed gases such as a high-pressure hydrogen and a compressed natural gas (CNG), various liquefied gases such as a liquid hydrogen, a liquefied natural gas (LNG), a liquefied petroleum gas (LPG) and the like are exemplified.
As a pressure vessel into which the various pressurized materials are filled, in general, one including a hollow container main body, a metallic mouthpiece portion attached to the container main body, and a valve attached to the mouthpiece portion is used. In the pressure vessel of this type, in general, an inner peripheral surface of the container main body is made up of a resin liner, and an outer peripheral surface of the liner is covered with a reinforcing portion made of a high-strength resin (such as fiber reinforced plastic: FRP).
The pressure vessel including the liner requires strength capable of withstanding filling of the high-pressure gas. Furthermore, in order to obtain a liner having excellent strength, it is considered that there is a need to reduce weld formed on the liner. The weld is considered to be likely to occur during molding when a flow path of the molten resin branches off and then the branched paths join with each other again. When the flow path of the molten resin branches off, a flow rate and a temperature of the molten resin are highly likely to be different for each of the branched paths. In such a case, it is hard to uniformly mix the joined molten resin. Therefore, in the obtained molded article, it is considered that resin regions adjacent to each other on a boundary of a weld line are in a state of being welded to each other.
Therefore, in a molded article in which weld occurs, it is considered that strength in the vicinity of the weld line is lower than that in the other portions. Because a liner is required to have high strength as described above, there is a need for a liner in which weld is hard to occur, and also a technique capable of molding a liner while suppressing an occurrence of weld.
It is considered that in order to suppress an occurrence of weld, it is effective to reduce branching off and joining of a molten resin in a cavity of a molding die. As technique of reducing branching off and joining of a molten resin in a cavity to suppress an occurrence of weld, molding a liner using a molding die having a film gate has been known (e.g., refer to Patent Literature 1). However, depending on the shape of the liner, it has not been possible to sufficiently suppress an occurrence of weld even when using the technique introduced in Patent Literature 1. For this reason, development of a technique to more effectively reduce an occurrence of weld is desired.